Ported Polygon->is_counter_clockwise() and rearranged code in .cpp files

xs/src/Polygon.cpp

@@ -0,0 +1,55 @@
+#include <myinit.h>
+#include "ClipperUtils.hpp"
+#include "Polygon.hpp"
+#include "Polyline.hpp"
+
+namespace Slic3r {
+
+SV*
+Polygon::to_SV_ref() {
+    SV* sv = newSV(0);
+    sv_setref_pv( sv, "Slic3r::Polygon", new Polygon(*this) );
+    return sv;
+}
+
+Lines
+Polygon::lines()
+{
+    Lines lines;
+    for (int i = 0; i < this->points.size()-1; i++) {
+        lines.push_back(Line(this->points[i], this->points[i+1]));
+    }
+    lines.push_back(Line(this->points.back(), this->points.front()));
+    return lines;
+}
+
+Polyline*
+Polygon::split_at_index(int index)
+{
+    Polyline* poly = new Polyline;
+    for (int i = index; i < this->points.size(); i++) {
+        poly->points.push_back( this->points[i] );
+    }
+    for (int i = 0; i <= index; i++) {
+        poly->points.push_back( this->points[i] );
+    }
+    return poly;
+}
+
+Polyline*
+Polygon::split_at_first_point()
+{
+    return this->split_at_index(0);
+}
+
+bool
+Polygon::is_counter_clockwise()
+{
+    ClipperLib::Polygon* p = new ClipperLib::Polygon();
+    Slic3rPolygon_to_ClipperPolygon(*this, *p);
+    bool orientation = ClipperLib::Orientation(*p);
+    delete p;
+    return orientation;
+}
+
+}